There's been a lot of talk lately about our position on removable storage and removable batteries in smartphones. Most of the discussion has centered around what we've said in podcasts or alluded to in reviews, so we figured it's a good time to have the complete discussion in one central location.

Let's get through the basics first:

All else being equal, removable storage and user replaceable batteries aren't inherently bad things. In fact, they can offer major benefits to end users. 

The key phrase however is "all else being equal". This is where the tradeoff comes in. On the battery front, the tradeoff is very similar to what we saw happen in notebooks. The move away from removable batteries allows for better use of internal volume, which in turn increases the size of battery you can include at the same device size. There are potential build quality benefits here as well since the manufacturer doesn't need to deal with building a solid feeling removable door/back of some sort. That's not to say that unibody designs inherently feel better, it's just that they can be. The tradeoff for removable vs. integrated battery is one of battery capacity/battery life on a single charge. Would you rather have a longer lasting battery or a shorter one with the ability the swap out batteries? The bulk of the market seems to prefer the former, which is what we saw in notebooks as well (hence the transition away from removable batteries in notebooks). This isn't to say that some users don't prefer having a removable battery and are fine carrying multiple batteries, it's just that the trend has been away from that and a big part of the trend is set based on usage models observed by the manufacturers. Note that we also don't penalize manufacturers for choosing one way or another in our reviews.

The tradeoffs are simple with an internal battery, the OEM doesn't need to include a rigid support structure on the battery to prevent bending, and doesn't need to replicate complicated battery protection circuitry, and can play with alternative 3D structures (so called stacked batteries) for the battery and mainboard as well. Personally, I'd rather have something that lasts longer on a single charge and makes better use of internal volume as that offers the best form factor/battery life tradeoff (not to mention that I'm unlikely to carry a stack of charged batteries with me). It took a while for this to sink in, but Brian's recommendation to charge opportunistically finally clicked with me. I used to delay charging my smartphone battery until it dropped below a certain level and I absolutely needed to, but plugging in opportunistically is a change I've made lately that really makes a lot of sense to me now.

The argument against removable storage is a similar one. There's the question of where to put the microSD card slot, and if you stick it behind a removable door you do run into the same potential tradeoff vs. build quality and usable volume for things like an integrated battery. I suspect this is why it's so common to see microSD card slots used on devices that also have removable batteries - once you make the tradeoff, it makes sense to exploit it as much as possible.

There's more to discuss when it comes to microSD storage however. First there's the OS integration discussion. Google's official stance on this appears to be that multiple storage volumes that are user managed is confusing to the end user. It's important to note that this is an argument targeted at improving mainstream usage. Here Google (like Apple), is trying to avoid the whole C-drive vs. D-drive confusion that exists within the traditional PC market. In fact, if you pay attention, a lot of the decisions driving these new mobile platforms are motivated by a desire to correct "mistakes" or remove painpoints from the traditional PC user experience. There are of course software workarounds to combining multiple types of storage into a single volume, but you only have to look at the issues with SSD caching on the PC to see what doing so across performance boundaries can do to things. Apple and Google have all officially settled on a single storage device exposed as a single pool of storage, so anything above and beyond that requires 3rd party OEM intervention.

The physical impact as well as the lack of sanctioned OS support are what will keep microSD out of a lot of flagship devices. 

In the Android space, OEMs use microSD card slots as a way to differentiate - which is one of the things that makes Android so popular globally, the ability to target across usage models. The NAND inside your smarpthone/tablet and in your microSD card is built similarly, however internal NAND should be higher endurance/more reliable as any unexpected failures here will cause a device RMA, whereas microSD card failure is a much smaller exchange. The key word here is should, as I'm sure there are tradeoffs/cost optimizations made on this front as well. 

The performance discussion also can't be ignored. Remember that a single NAND die isn't particularly fast, it's the parallel access of multiple NAND die that gives us good performance. Here you're just going to be space limited in a microSD card. Internal NAND should also be better optimized for random IO performance (that should word again), although we've definitely seen a broad spectrum of implementation in Android smartphones (thankfully it is getting better). The best SoC vendors will actually integrate proper SSD/NAND controllers into their SoCs, which can provide a huge performance/endurance advantage over any external controller. Remember the early days of SSDs on the PC? The controllers that get stuffed into microSD cards, USB sticks, etc... are going to be even worse. If you're relying on microSD cards for storage, try to keep accesses to large block sequentials. Avoid filling the drive with small files and you should be ok.

I fully accept that large file, slow access storage can work on microSD cards. Things like movies or music that are streamed at a constant, and relatively low datarate are about the only things you'll want to stick on these devices (again presuming you have good backups elsewhere).

I feel like a lot of the demand for microSD support stems from the fact that internal storage capacity was viewed as a way to cost optimize the platform as well as drive margins up on upgrades. Until recently, IO performance measurement wasn't much of a thing in mobile. You'd see complaints about display, but OEMs are always looking for areas to save cost - if users aren't going to complain about the quality/size/speed of internal storage, why not sacrifice a bit there and placate by including a microSD card slot? Unfortunately the problem with that solution is the OEM is off the hook for providing the best internal storage option, and you end up with a device that just has mediocre storage across the board.

What we really need to see here are 32/64/128GB configurations, with a rational increase in price between steps. Remember high-end MLC NAND pricing is down below $0.80/GB, even if you assume a healthy margin for the OEM we're talking about ~$50 per 32GB upgrade for high-speed, high-endurance internal NAND. Sacrifice on margin a bit and the pricing can easily be $25 - $35 per 32GB upgrade.

Ultimately this is where the position comes from. MicroSD cards themselves represent a performance/endurance tradeoff, there is potentially a physical tradeoff (nerfing a unibody design, and once you go down that path you can also lose internal volume for battery use) and without Google's support we'll never see them used in flagship Nexus devices. There's nothing inherently wrong with the use of microSD as an external storage option, but by and large that ship has sailed. Manufacturers tend to make design decisions around what they believe will sell, and for many the requirement for removable storage just isn't high up on the list. Similar to our position on removable batteries, devices aren't penalized in our reviews for having/not-having a removable microSD card slot.

Once you start looking at it through the lens of a manufacturer trying to balance build quality, internal volume optimization and the need for external storage, it becomes a simpler decision to ditch the slot. Particularly on mobile devices where some sort of a cloud connection is implied, leveraging the network for mass storage makes sense. This brings up a separate discussion about mobile network operators and usage based billing, but the solution there is operator revolution.

I'm personally more interested in seeing the price of internal storage decrease, and the performance increase. We stand to gain a lot more from advocating that manufacturers move to higher capacities at lower price points and to start taking random IO performance more seriously.

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  • Klug4Pres - Saturday, December 21, 2013 - link

    "So do you propose that things will get better if we encourage every OEM to stick with 16GB of NAND and a battery that lasts 3 hours as the baseline, as long as there's a microSD slot and the battery is swappable?"

    No, what I would suggest is that, among a variety of different offerings, including completely sealed devices for the unibody/monocoque fetishists, there is room for non-Samsung devices to come with:

    (i) A removeable battery of at least 2500 mAh as standard, with official and aftermarket replaceable back covers giving options for larger batteries;
    (ii) Fast internal flash offered at different price points for 16/32/64/128GB
    (iii) Hot-swappable microSD slot up to 128GB
    (iv) USB 3.0 OTG, allowing simultaneous charging and attachment of HDMI out, and USB hubs, both powered and unpowered
  • repoman27 - Wednesday, November 27, 2013 - link

    Actually, the burden is on you. You'll need to either show that Brian and Anand's premises are untrue, or that their argument is invalid if you want to disprove them. I have not seen anything in these comments that refutes so much as a single statement they made.

    I challenge you to disprove any of their conclusions.
  • Hairs_ - Thursday, November 28, 2013 - link

    All of Anand and Brian's criticisms about removeable storage/parts list "potential tradeoffs" or "potential compromises".

    The truth is that the difference between a well-engineered device and a poorly engineered device in terms of "in hand feel" is likely nothing to do with replaceable parts and far more to do with an overall cost-cutting approach in terms of materials and construction methods. Talking about "potential" this and "possible" that goes both ways.

    "Potentially" the OEM's are exaggerating these challenges and compromises to favoured reviewers in order to get them on side so that anti-consumer price gouging can continue. Does a HTC One feel better in the hand than the Galaxy S3? Sure. Is that down to a micro SD slot? No, blatently not.

    Here's a simple conundrum for you:
    If battery doors, MicroSD slots, GSM sized SIMs and replaceable parts lead to unacceptable engineering tradeoffs and lower device quality, why did Apple have to spin that users were "holding it wrong" when their poor engineering decisions around the antenna for the 4 were revealed?

    Bad engineers, cost cutting regimes, poor quality control, and pressures of time to market are all more significant factors in creating devices with poor build quality and reliability than any of the "issues" raised by Anand and Brian in this article.
  • repoman27 - Monday, December 2, 2013 - link

    No. Anand and Brian primarily cite incontrovertible compromises inherent to two very specific features of smartphones, whereas their critics cite potential benefits or use cases which make the trade-offs involved preferable. (Which is not to say that there are not valid points raised by both sides.)

    Your simple conundrum is a non sequitur mixed with bait for any Apple fanbois. It is also largely irrelevant to the topics addressed by the original post.
  • Hairs_ - Monday, December 9, 2013 - link

    What "incontrovertible" claims do they make about replacement batteries and SD card slots?

    " The move away from removable batteries allows for better use of internal volume, which in turn increases the size of battery you can include at the same device size. There are potential build quality benefits here as well since the manufacturer doesn't need to deal with building a solid feeling removable door/back of some sort. That's not to say that unibody designs inherently feel better, it's just that they can be."

    Directly quoting from the article, if the words "can" and "potential" are confusing to you, perhaps you should stop analysing other people's posts.

    Are you suggesting that the Nokia 3310 was a phone with poor build quality based on its removable battery and full size SIM card?

    My conundrum is very simple, you're correct. Apple produced a device with none of the "tradeoffs" you, Anand and Brian deride as detrimental to the quality of a device, but made a severe balls of a very simple engineering problem, ie radio attenuation. Apple made a "tradeoff" between aesthetics, materials and physics. Unfortunately, they chose the first two over the third, and the third spanked them for it. If you don't like the apple example, pick another manufacturer. They've all made various engineering design mistakes over the years, but the number which can be pinned on SD cards is absolutely minimal.

    The build quality of a device does not have any meaningful relationship to the inclusion of user-replaceable batteries, and the companies who are suggesting that it does are, very simply, telling porkies. Replaceable batteries and expandable storage were never issues for well over a decade. Their denigration as features has come at a time when, coincidentally, some manufacturers have discovered that removing them results in the ability to price-gouge consumers on basic additions like storage capacity and charging "features".
  • repoman27 - Monday, December 16, 2013 - link

    I love how you selected a quote that perfectly illustrates my point and then tried to claim that the words "can" or "potential" are somehow problematic. The first sentence is based on deductive reasoning that is both valid and sound, and neither you nor any other commenter here has done anything to disprove it. The second sentence presents an inferential claim based on inductive reasoning that is both strong and reliable. The third sentence is poorly written, but is merely meant to underscore that the second sentence does not imply that all unibody designs feel better than all non-unibody designs.

    You then go on to provide an example that justifies Anand's inclusion of that third sentence. His point was that while there are obviously examples of well made phones with removable backs, it's still easier to make a solid feeling phone if you don't have to worry about that aspect of the design.

    Apple's antenna design on the iPhone 4 resulted in excessive signal attenuation for many users. That has zero bearing on the tradeoffs that come with incorporating microSD card slots or user removable batteries in a smartphone. What exactly is your argument here? That because no one has yet to completely bollox a design specifically through the inclusion of a microSD card slot, therefore all smartphones should have them?
  • stop-a - Tuesday, November 26, 2013 - link

    I just feel bad that my Note2 and Korean LG G2 are having swappable batteries, yet I could easily use the stock battery to last for more than 1day. This must be violating Anand's golden rule that non-swappable batteries must last longer than swappable ones. According to Anand, you couldn't have a phone with long last battery while it is also swappable. I feel Samsung is not playing up to Anand's rule, and by Anand's logic Samsung must be punished.
  • rxzlmn - Tuesday, November 26, 2013 - link

    1. A decent speed microSD with 64 gigs cost me about 45 dollars (15mb/s write, 35 read). Never, ever will manufacturers charge you just 45 dollars to go from 16 gig to 80 gig. They want to earn money.

    2. My data plan is capped at 3 gig. Previously I had a much larger cap and thus was using Spotify to stream, accumulating well over 10 gig data per month. So, I download playlists I follow now on Wifi. I don't wanna think about how much storage I need for that.

    3. I don't see how an SD slot is ruining my Z1's body design.

    4. If you don't want to put in an SD card, just don't do it. The cost to put in a slot is so little it is dumb to omit it.

    5. Where are all those tradeoffs this article talks about to be seen IN REALITY, on those devices that have SD slots?
  • Andrewv21 - Tuesday, November 26, 2013 - link

    Another design/construction issue is wireless charging: devices with battery doors, removable backs, etc. are generally more likely to give me the option of dropping in a receiver coil for Qi or whatever charge system I want. Hopefully the industry will soon be to the point where most devices have a widely accepted wireless charging receiver built in regardless of battery/SD card options, but as it stands right now 'sealed' devices are mostly left with clunky external coils built into oversized cases as the only option for wireless charger compatibility.
  • jmunjr - Wednesday, November 27, 2013 - link

    I simply cannot live with a replaceable battery. I use extended batteries which last all day regardless how I use my phone and I swap it with another fully charged battery when I choose. I never have to worry about charging my phone because I am always charging my batteries. A phone should never have to be charged, but the batteries should.

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